import re
from dataclasses import dataclass
from datetime import datetime
from decimal import ROUND_HALF_UP, Decimal
from typing import Optional

_PLACEHOLDER_RE = re.compile(r"\{\{\s*(\w+)\s*\}\}")


def render_template(text: str, variables: dict[str, str]) -> str:
    return _PLACEHOLDER_RE.sub(lambda m: str(variables.get(m.group(1), m.group(0))), text)


def format_datetime_da(dt: datetime) -> str:
    return dt.strftime("%d-%m-%Y kl. %H:%M")


@dataclass
class CatalogRow:
    category_name: str
    wine_name: str
    unit_price_eur: Decimal
    ordered_quantity: Optional[int]  # None = ikke bestilt, vises tomt


def render_order_receipt_html(rows: list[CatalogRow]) -> str:
    """rows skal være for-sorteret efter (kategori.sort_order, vin-id) —
    denne funktion grupperer blot konsekutive ens kategorinavne under
    én overskrift, ligesom den gamle Kvitering-mail."""
    html_parts = ['<table style="border-collapse:collapse;width:100%;">']
    current_category = None
    for row in rows:
        if row.category_name != current_category:
            html_parts.append(
                f'<tr><th colspan="3" style="text-align:left;padding-top:12px;">{row.category_name}</th></tr>'
            )
            current_category = row.category_name
        qty_display = str(row.ordered_quantity) if row.ordered_quantity else ""
        html_parts.append(
            f'<tr><td style="padding:2px 8px;width:40px;">{qty_display}</td>'
            f'<td style="padding:2px 8px;">{row.wine_name}</td>'
            f'<td style="padding:2px 8px;text-align:right;">{row.unit_price_eur:.2f}</td></tr>'
        )
    html_parts.append("</table>")
    return "".join(html_parts)


def compute_order_total_eur(rows: list[CatalogRow]) -> Decimal:
    """Kun de faktisk bestilte linjer tæller med i totalen — resten af
    kataloget er kun til visning. Ingen afrunding her (fuld præcision
    bevares til evt. DKK-omregning)."""
    return sum(
        (r.unit_price_eur * r.ordered_quantity for r in rows if r.ordered_quantity),
        Decimal("0"),
    )


def format_currency(amount: Decimal) -> str:
    """Eneste sted afrunding sker — til visning, normal matematisk
    afrunding (ikke Decimal's ROUND_HALF_EVEN-standard)."""
    return str(amount.quantize(Decimal("0.01"), rounding=ROUND_HALF_UP))